Drill collar with helical grooves



July-13, 1965 E. P. ARNOLD 3,194,331

DRILL COLLAR WITH HELICAL GROOVES Filed May 22, 1964 f P. 14/77 0 /a INVENTOR.

BY g

United States Patent r 3,194,331 I DRILL COLLAR WITH HELICAL GRO'OVES Edward P. Arnold, Arnold Pipe Rental Company, R0. Box 4014, Corpus Christi, Tex.

Filed May 22, 1964, Ser. No. 369,558 2 Claims. (Cl. 175-323) This invention relates to the rotary drilling of deep wells and more particularly to improved drill collars to be coupled in multiple succession at the lower end of a tubular drill string for controlling weight on the bit and for co-operation with the well bore wall in minimizing hole deviation and stuck drill collars and also for facilitating wash-over operations. v

An object of the invention is to provide a drill collar whose peripheral surface contains an improved helical groove formation to interrupt longitudinal continuity of the surface and materially reduce collar bearing contact area and to provide an effective cutting edge which can on occasion act as a broach against troublesome bore wall surfaces. 7 p v A further object of the invention is to provide a tubular drill string member-having one or more peripheral grooves extending throughout the length of an intermediate large diameter portion whose diameter is only slightly smaller than the drill bit and therefore the wellhole so that the surrounding annulus space for drilling fluid approximates the size of the internal bore through the collar and which grooves freely communicate in open ended relation with opposite end reduced diameter portions of the drill string members so that the grooves and the longitudinally spaced apart annular recesses afforded by the reduced diameter portions co-operate in enlarging the annulus flow space and increase the collar surface area which will be spaced from contact with the wall face of the wellhole. I

Other objects and advantages will become apparent from the following specification andreference to the accompanying drawing, wherein FIG. 1 is avertical section of a small length of drilled earth containing a drill string;

FIG. 2 on a larger scale is a view partly in elevation and section of collar fragments;

FIG. 3 is a transverse section on a still larger scale, and

FIG. 4 is a vertical section of a well bore containing a modified'collar configuration.

In conventional rotary drilling operations, a string of pipe sections, each about thirty feet long, suspended from the surface and extended through the wellhole, is H I driven at the surface normally in a clockwise direction and drives a drilling bit on bottom with drilling fluid being pumped to the bit through the tubing string and returning through the annulus space surrounding the pipe. Usually, in deep wells the upper pipe sections are held in tension to control weight on the bit and the lower sections, just above the bit and often as many asthirty in number, have thicker, stiffer and heavier walls and are known as drill collars whose purposes, among others, are to weight the bit and direct it on a straight course. Downhole characteristics and operational conditions sometimes result in hole deviation, the formation of key seats and a tendency toward the pipe becoming stuck for any one or more of several recognized causes. One cause of pipe sticking has been attributed to drilling fluid pressure acting laterally against the drill collars, Which may be in bearing contact with the wall of a formation whose pressure is less than that of drilling fluid pressure. Practices to lessen sticking have been many, including continuous rotation, oil spotting, decreased fluid weight, stabilizers, drilling collar surface configurations,

3,194,331 Patented July 13, 1965 which also facilitate wash-over operations during fishing and in some instances provide a broaching or cutting onto the formation for clearing a stuck point or a potentially sticking condition. None affords the complete answer to the problems and loss of equipment in wellholes continues.

A drilling string with improved peripheral surface configuration which not only breaks up continuity of bearing surface also provides a useful cutting action when required to minimize hole deviation, sticking problems, loss of pipe from twist-elf and fishing costs, will now be described.

Referring first to FIG. 2, there is illustrated a hollow drill string pipe section or drill collar 1 consisting of an elongate tubular number of circular cross section having a central bore 2 therethrough as well as the conventional screw threaded pin and box formations at opposite ends for end to end coupling in a string of hollow pipe sections as in FIG. 4. For handling convenience, drill collars are usually about thirty feet long and of selected outside diameter of about two thirds of hole diameter. The annulus space surrounding such drill collars will be of a volume capacity or size somewhat in excess of the size of the central bore through the tubing string. A central bore of two and three fourths inches is common for a six-inch drill collar whose wall thickness will be about one and five eighths inches, and thirty feet of such a drill collar will weigh a little more than twenty-four hundred pounds. These figures are mentioned as exemplary.

To conserve weight and stiffness while providing downwardly facing peripheral working edges associated with axially spaced apart and reasonably large longitudinal gaps in bearing surface continuity, it is here proposed to incorporate a special and purposefully designed and effective groove shape in the outside of a drill collar and around its circumference. Preferably, a number such as four grooves 3 are cut to follow helical paths, each with a pitch of forty-two inches as measured longitudinally of the drill collar. Each groove 3 is particularly defined by a V-bottom and, as seen in vertical section in FIG. 2, its angularly related sides constitute a long leg 4 and a short leg 5 which project inwardly from the collar periphery in convergent relation one to another in a manner to resemble an inverted L and with the upper short leg 5 constituting a downwardly facing shoulder, making an acute angle to a horizontal radial plane trans versely of the collar and terminating at its outer edge in a sharp corner relationship with the collar peripheral surface. Its long side or leg 4 runs downwardly at an obtuse angle with the short leg 5 of the groove for a distance to insure optimum clearance or gap length. In one preferred embodiment, the distance across each of such helically directed grooves 3 measures four and a half inches longitudinally on a six-inch drill collar and the intervening uncut periphery will be six inches long, yielding a resultant reduction of about forty-three and three tenths percent of the peripheral bearing surface.

To obtain the described groove shape, a rotating cutter on an axis transverse to the collar axis turns across a circumferential Zone of the collar periphery and removes metal from a circular wall segment. The design of the revolving cutter forms a V-groove which, as seen in the transverse section of FIG. 3, is about two inches wide and to a depth at the point of leg convergence of about three tenths of an inch and the short leg 5 of the V-groove projects inwardly from the collar periphery at an abrupt angle preferably in the range of eighteen degrees to twenty-two degrees but in any event less than forty degrees from a radial line intersecting the outer end of the short leg. Such angle is indicated at a in FIG. 3 by projection collar.

lines. Here, again, thesurface of the long leg 40f the V-groove projects generally circumferentially' at an obtuse angle to the short leg andvfor the required distance to provide the: clearancefgap previously mentioned. The

circumferentialdirection of the long. leg 4 as viewedin -FIG.. 3, follows a line tom'erge; smoothlyinto.theqgieriph-v eral surface of the ,collar Without an abrupt bend at their intersection; V 7

Thus the short legS", as seen in transverse' section, is

at the leading 'endof the groove 3 during normally clockas viewed in vertical section, FIG.,2, and can shear incl dent t-o descending travel of the, drill string. Such descending travel'not only occurs during normal drilling is at least equal to the combined flow areas within all the but also on down strokes: of drill, string reciprocation, when greater broaching action is desirable. A broachingf and, bore face cutting action may-be obtained by con-t trolled reverse rotation and without longitudinal travel ;of the drill string since the sharp angle of the shortz leg ,is then the trailing edge of the groove. The reference f to :broachin'g action assumes that some portion of the collarhas' bearingrcontact with the wall of the'wellhole.

The length of such contact mayvary froma short offset in hole direction up to the over-all length of the number of drill collars employed.

In,thisiconnectiommention should be made that desired 50 collanstifrness and controlled weight application for hole straightness is affected ,by difficult fiormation characteristics such as those withgdips of forty degrees or less;

Crooked holes are experienced in tilted laminar shale and ,sandstone as illustrated 'at 7 in FIG. 1. Fracture of rock occurs perpendicular to the bedding plane and the bottom wherein the 'bitI 6 tends, to drill updip. or into the hill. i

portions of upwardly inclined layers on the uphillor the s somewhat as diagrammed in FIG. 1 and as more then woughly discussedin World Oil, page 71, March 1963. .In

such situations, contact with the downhill; side of the well wall by'theherein disclosed V-"gr-ooved drill collars will occur and during descent, of the collars; a desired broaching and cutting away of the stepped bore, .wall will avoid kejy seatproblems zandsmooth out sharp offsets in z hole. direction. 7

, 'proximates the size of the; central bore 12 through the Hence the collar ,willrnore readily come into hearing contact with the wall of the holefor guiding the direction of drilling and minimizing, deviation from an V intended straight course. 'Again, to break up'surface continuity and to compensate forreduced annulus clearance and provide flow size around the collar in' excess of volumetric capacity of the central bore through the drill string, there are provided a group of 'helically directed 'V-grooves 13' shaped as previously described and, in addition, all the grooves open into and communicate at both" ends with reduced diameter portions 18 and 1?; at oppo- 'site pin and box end connecting regions of, each drill eral surfaceof the medial portion ofi the collar and to a 7 "depth, that the, added annular clearance within the recess helical grooves."

In addition to increasing annulusflow-size,,theannular recesses at the ends 18 and 19 co-operate with the grooves in breaking 'up ,and jrnaterially"decreasingthe' errterior 1 surface bearing' area on;the drill collar periphery. By making the annular recess at the boxend eighteen inches] long and the annular recess'atthe pin endjtwelve' inches, 5 longfthere wouldbe a total-oftwo and; a half-feet in, length taken out of the-;bearingarea ofeachcollarand iin a group of thirty end to end "coupled' c'ollars, each v thirty feetlong, these recesses, :locatedfat axially*'spaced intervals, account for a :combined seventy-five 'feet.,to reduce surface contact withthe bore walls; That overall' length plus the .total lon'gitudinalgfootageprovidedzby groove clearancesrwill be substantially equal to thefuncut bearing. area measured longitudinally andfanyfportion; of, which might, contactwith the wall pf: the well bore. Be-:

' cause of the increased weightand stiffnessrin such oversize, collars, one ormore-additional annular recesses ieould. properly beecutintermediate' and axially'spaced fromtthe smaller'diameterlend portions fora further reduction in 1 bearing yarea without tobjectionablegloss ofineces sary' weight and stiffness .iri the drill gc ollar section of the f tubular string.

During drilling 'grotationcofgthe tubing ;string,";jretur11 flow of drilling fluid upwardly throughthe-anmuusf space f .will react downwardly on the upwardly facing groove. 2 surfaces and apply a helpful loadonythegbitsupplemental to drill, Ycollarjweightingk :{Because of lsuchfadditional I; loading on the-bit,"it;willfbe feasibleingsome-cases to; p cut down the number of drill collarst requiredand replace? theml-with less costlydrill pipe, Similar cost Fsavings, will berealized through;the use of oversize drill collars}. 1 having the improved surface configurati nsde'ScIibed' and without. sacrifice of advantages Itg willibe'notedthat;

the weight of metal removed hyigroove :form'ation will be less in relationtdtotal collar'weight in therc'ase of-g-a 1 large diameter oversize icollar'than inacollarof convene i tional size heretofore {used fora given diameter: hole;

By' comparison, seventeen 1Vgrooved; ,collars'iwh-osef dh' l mensions are four; and threeqqua'rters inches outside gdit ameter, two and'one quarter inches inside; diameterand; V

' thirty feet longiwill approxirnatethe weight of andreplace a twenty-one conventional,fcollars :whosejidimensions are;

fo'uriand one 1eighth inchesfoutside} diameter,twoinchesa; inside vdiameter. and tthirty feet long. 3 Comparisonifofif;

hydraulics'of the sametwoiglrillicollarstrings islalsdinjterestingl; Assuming not pressure loss attributable-to fluid passage through the bit and considerin'g the same drillingmud characteristics, eirculation"rate',and hole sizes, calculationsindicate a decrease offorty-three and nine tenths percent in;P, essure-1o'ss with the groovedcol-'f lar string as against; pressure loss Wlthf the conventional: string based on 'pressure differentials from; thqlimerin- V jecteddrillingvmud enters-"the inside. .b o're ofthe upper:

most collar of ,each string ,until the ;same fiuidfrise s through theannulris and past the identicalspot outside -i the string, Lower loss in annulus pressure affords surer entrainment and clearing ofacuttings especially the V removalof the "larger and heavier tfragmentsi from ,bit: .7

working interference-at the'formation facebeingdrilled While. the foregoing has been specific todetailistrucr.

ture, it is to be understood that suchvariations and modi v fications can be'made as come within-thescope of; the appended'claims;

What is m d is: ,r

, 1.1An integral elongate tubular'member having means at opposite ends 'for' connection ina rotary drill string and at leastione helical grooveinitsfouter peripheral jsurface, which isof V shape insection transversely'ofjiu. V the, member, the leg of thegV-shapeVflhichis located at;

the 'leadingfedg e of the groove during drill stringrotation in the normal drilling ;direction"he ing,v on the order of about thirteen percent'aslong asiithe otherleg and, pro-- jecting inwardly of said peripheral surface at an angle of less than forty degrees to a radial line at said leading edge of the groove.

2. An integral elongate tubular member having means at opposite ends for connection in a rotary drill string and at least one helical groove formation in its outer peripheral surface, said groove formation in section transverse- 1y of the member being defined by a pair of inwardly converging side surfaces of which one is relatively shorter than the other and projects inwardly from said peripheral surface and from the groove leading edge in relation to the direction of rotary drilling, at an acute angle of about twenty degrees with a radial line intersecting said leading edge, the other of the side surfaces extending at an obtuse angle from the shorter side surface and on a line which merges smoothly Without an abrupt cutting edge into said peripheral surface at the trailing end of the groove, said shorter side surface constituting the top of the groove in any section longitudinally of the member and projecting at an acute angle to its intersection with said peripheral surface to provide a downwardly directed cutting edge portion.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Bobo: Keys to Successful Competitive Drilling, Houston, Tex., Gulf Pub. Co., 1958 (pp. 131 and'132).

CHARLES E. OCONNELL, Primary Examiner.

20 BENJAMIN HERSH, Examiner. 

1. AN INTEGRAL ELONGATE TUBULAR MEMBER HAVING MEANS AT OPPOSITE ENDS FOR CONNECTION IN A ROTARY DRILL STRING AND AT LEAST ONE HELICAL GROOVE IN ITS OUTER PERIPHERAL SURFACE, WHICH IS OF V-SHAPED IN SECTION TRANSVERSELY OF THE MEMBER, THE LEG OF THE V-SHAPE WHICH IS LOCATED AT THE LEADING EDGE OF THE GROOVE DURING DRILL STRING ROTATION IN THE NORMAL DRILLING DRICTION BEING ON THE ORDER OF ABOUT THIRTEEN PERCENT AS LONG AS THE OTHER LEG AND PROJECTING INWARDLY TO SAID PERIPHERAL SURFACE AT AN ANGLE OF LESS THN FORTY DEGREES TO A RADIAL LINE AT SAID LEADING EDGE OF THE GROOVE. 